Invariant natural killer T-cells (NKT) are a subset of T-cells that are implicated in a broad range of diseases. In some circumstances they can enhance the response to infection (Kinjo, Illarionov et al. 2011) and cancer (Wu, Lin et al. 2011) but also possess the ability to suppress autoimmune disease (Hong, Wilson et al. 2001) and type II diabetes. Activation of NKT cells can also lead to undesirable immune responses as related to allergy, (Wingender, Rogers et al. 2011) autoimmunity (Zeng, Liu et al. 2003) and atherosclerosis (Tupin, Nicoletti et al. 2004).
Unlike conventional T-cells that are restricted by major histocompatibility complex (MHC) molecules that present peptide antigens, NKT cells are uniquely restricted by CD1d proteins (Bendelac, Savage et al. 2007). CD1d proteins belong to the CD1 family that contains five members, CD1a-e. Like MHC molecules, the CD1 family members all contain an antigen binding region that is flanked by two anti-parallel α-helices that sit above a β-sheet. Unlike MHC molecules, the binding region of the CD1 proteins contain two large hydrophobic binding pockets that are suited to bind lipid antigens rather than peptide based antigens (Li, Girardi et al. 2010). α-Galactosylceramide (α-GalCer) is the most studied NKT cell antigen and potently activates human and mouse NKT cells (Kawano, Cui et al. 1997). In animal studies, α-GalCer is reported to be useful in the treatment of a number of diseases including cancer, (Morita, Motoki et al. 1995; Motoki, Morita et al. 1995) and autoimmune disease (Hong, Wilson et al. 2001). The compound has also been shown to function as a potent vaccine adjuvant in the treatment and prophylaxis of cancer and infectious disease (Silk, Hermans et al. 2004). This adjuvant activity has been attributed to stimulatory interactions between activated NKT cells and dendritic cells (DCs), the most potent antigen-presenting cells in the body. As a consequence, the DCs are rendered capable of promoting strong adaptive immune responses (Fujii, Shimizu et al. 2003; Hermans, Silk et al. 2003).
Although α-GalCer has considerable biological activity it does have limitations such as poor solubility, (Ebensen, Link et al. 2007) lack of efficacy in human clinical trials, (Giaccone, Punt et al. 2002) promotion of T-cell anergy (Parekh, Wilson et al. 2005) and the generation of both Th1 and Th2 cytokines that may contribute to mixed results in model studies.

It is therefore an object of the invention to provide novel compounds useful as agents for treating diseases or conditions relating to infection, autoimmune disease, atopic disorders or cancer, or to at least provide a useful alternative.